From dd94ac5a9379ca5abc4bfc0a5efd2c3d6f373435 Mon Sep 17 00:00:00 2001
From: Pierre Jeanjean <rhiobet@gmail.com>
Date: Fri, 9 Dec 2022 07:45:55 +0100
Subject: [PATCH] Day 9

---
 day09/common/bridge.go | 116 +++++++++++++++++++++++++++++++++++++++++
 day09/ex1/main.go      |  23 ++++++++
 day09/ex2/main.go      |  23 ++++++++
 3 files changed, 162 insertions(+)
 create mode 100644 day09/common/bridge.go
 create mode 100644 day09/ex1/main.go
 create mode 100644 day09/ex2/main.go

diff --git a/day09/common/bridge.go b/day09/common/bridge.go
new file mode 100644
index 0000000..50c0f6e
--- /dev/null
+++ b/day09/common/bridge.go
@@ -0,0 +1,116 @@
+package common
+
+import (
+	"bufio"
+	"strconv"
+)
+
+
+type Direction int
+
+const (
+  Right Direction = iota
+  Left
+  Down
+  Up
+)
+
+
+type Movement struct {
+  direction Direction
+  distance int
+}
+
+
+type Position struct {
+  x int
+  y int
+}
+
+func NewPosition(x int, y int) *Position {
+  return &Position{x, y}
+}
+
+
+type Grid struct {
+  rope []Position
+  head *Position
+  tail *Position
+}
+
+func NewGrid(size int) *Grid {
+  rope := make([]Position, size)
+  return &Grid{rope, &rope[0], &rope[size-1]}
+}
+
+func (grid *Grid) Move(movement Movement) (map[Position]struct{}) {
+  visitedTail := make(map[Position]struct{})
+
+  visitedTail[*grid.tail] = struct{}{}
+
+  for i := 0; i < movement.distance; i++ {
+    switch movement.direction {
+      case Right:
+        grid.head.x++
+      case Left:
+        grid.head.x--
+      case Up:
+        grid.head.y--
+      case Down:
+        grid.head.y++
+    }
+    grid.Update()
+    visitedTail[*grid.tail] = struct{}{}
+  }
+
+  return visitedTail
+}
+
+func (grid *Grid) Update() {
+  for i := 1; i < len(grid.rope); i++ {
+    head := &(grid.rope[i-1])
+    tail := &(grid.rope[i])
+    if tail.x < head.x - 1 || tail.x > head.x + 1 ||
+       tail.y < head.y - 1 || tail.y > head.y + 1 {
+      if tail.x == head.x {
+        tail.y = (tail.y + head.y) / 2
+      } else if tail.y == head.y {
+        tail.x = (tail.x + head.x) / 2
+      } else if tail.x == head.x - 1 || tail.x == head.x + 1 {
+        tail.x = head.x
+        tail.y = (tail.y + head.y) / 2
+      } else if tail.y == head.y - 1 || tail.y == head.y + 1 {
+        tail.x = (tail.x + head.x) / 2
+        tail.y = head.y
+      } else {
+        tail.x = (tail.x + head.x) / 2
+        tail.y = (tail.y + head.y) / 2
+      }
+    }
+  }
+}
+
+
+func Parse(scanner bufio.Scanner) []Movement {
+  movements := []Movement{}
+
+  for scanner.Scan() {
+    line := scanner.Text()
+
+    var movement Movement
+    distance, _ := strconv.Atoi(line[2:])
+    switch line[0] {
+      case 'L':
+        movement = Movement{Left, distance}
+      case 'R':
+        movement = Movement{Right, distance}
+      case 'U':
+        movement = Movement{Up, distance}
+      case 'D':
+        movement = Movement{Down, distance}
+    }
+    movements = append(movements, movement)
+  }
+
+  return movements
+}
diff --git a/day09/ex1/main.go b/day09/ex1/main.go
new file mode 100644
index 0000000..7620986
--- /dev/null
+++ b/day09/ex1/main.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+  "bufio"
+  "fmt"
+  "os"
+  "aoc2022/day09/common"
+)
+
+func main() {
+  movements := common.Parse(*bufio.NewScanner(os.Stdin))
+  grid := common.NewGrid(2)
+  visited := make(map[common.Position]struct{})
+
+  for _, movement := range movements {
+    tailVisited := grid.Move(movement)
+    for position := range tailVisited {
+      visited[position] = struct{}{}
+    }
+  }
+
+  fmt.Println(len(visited))
+}
diff --git a/day09/ex2/main.go b/day09/ex2/main.go
new file mode 100644
index 0000000..98fdb95
--- /dev/null
+++ b/day09/ex2/main.go
@@ -0,0 +1,23 @@
+package main
+
+import (
+  "bufio"
+  "fmt"
+  "os"
+  "aoc2022/day09/common"
+)
+
+func main() {
+  movements := common.Parse(*bufio.NewScanner(os.Stdin))
+  grid := common.NewGrid(10)
+  visited := make(map[common.Position]struct{})
+
+  for _, movement := range movements {
+    tailVisited := grid.Move(movement)
+    for position := range tailVisited {
+      visited[position] = struct{}{}
+    }
+  }
+
+  fmt.Println(len(visited))
+}